There are two primary objectives for the glycophorin A-based somatic mutation analysis project. The first objective is to determine the magnitude and types of somatic mutational damage in liquidators exposed to radiation from the Chernobyl nuclear power accident as measured by the glycophorin A (GPA) assay. Analysis will be performed on blood samples from Russian liquidators with low-dose exposures and Russian controls, and will include measurements of the frequency of both hemizygous NO and homozygous NN variant erythrocytes. Measurements of the frequencies of somatic cell mutations at the GPA locus will be correlated with different indicators of genetic damage from other projects in the program project to provide a comprehensive analysis of genetic damage and potential health consequences in the liquidator population. The second objective is to utilize GPA data from the Chernobyl liquidator population to determine optimal strategies for detecting low-dose radiation exposures that may be applicable for future studies in other populations. Personal history data from questionnaires will be utilized to identify factors that contribute to inter-individual variability. Statistical procedures will be identified to adjust for confounding factors and facilitate differentiation between exposed and control populations. Results from the GPA assay will be compared with the results from other biodosimeters in the program project to determine the relative sensitivity and reliability of the different methods, and the power of the combined data for detecting low-dose radiation exposure in humans.